* On selecting "Finish partitioning and write changes to disk",
partman shows (where /dev/foo_p1 is the first partition device on
the corresponding disk device):

Error informing the kernel about modifications to partition
/dev/foo_p1 -- Invalid argument. This means Linux won't know
about any changes you made to /dev/foo_p1 until you reboot -- so
you shouldn't mount it or use it in any way before rebooting.

ERROR!!!

* Selecting "Ignore" shows the same dialogue message for all other
partitions that were generated by partman

From information provided in a follow-up installation report (#462809, now
merged with this report) it looks as if partman-auto may be somehow
creating an invalid partitioning setup. Reason I suspect this is that using
the "manual partitioning" option in partman, submitter _was_ able to create
a valid setup.

Tracking down this issue will most likely require porter effort, therefore
tagging help.